The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles. As HDD areal density increases, the dimensions of both bits and the readback sensor must become smaller and smaller. However, requirements for media overcoats and lube have made it difficult to scale down the slider fly height in proportion to the reduction in reader dimensions, creating a discrepancy between the physical reader track width and an effective “magnetic read width” because of the interaction between stray magnetic flux from tracks adjacent to the written track and the read head.
One proposed solution to solve this problem is to deposit high permeability material on the sides of the read head to act as side shields to absorb the stray flux from adjacent tracks and bring the magnetic read width more in line with the physical track width, which may help reduce some of the constraints in fabricating the heads as well as help overall signal-to-noise ratio (SNR) by allowing for a larger physical track width (e.g., larger free layer magnetic volume would reduce magnetic noise in a read device).
One issue with implementing this strategy is that the side shields would replace the traditional hard bias material in the read head, which is required for standard sensor operation. The shield material may double as a hard bias source, but materials with good shield characteristics tend to have lower coercivity and anisotropy, and less available magnetic field for sensor stabilization. Another option is to put the hard bias on a back edge of the read sensor, but this too would decrease the available field for stabilization as the hard bias would be located away from the plane of the sensor.
Accordingly, one solution is to use a read sensor that does not require hard bias in the conventional location (i.e., adjacent to the sensor edges which define the track width). One such sensor is called a scissor sensor, and includes two free magnetic layers that are oriented at about 45° with respect to one another by placing the hard bias at the back edge of the sensor and orienting the hard bias in a transverse direction (as opposed to a longitudinal direction as for conventional sensors). This allows for the fabrication of side shields without affecting sensor performance (see, for example, U.S. Pat. No. 7,869,165 and U.S. Patent Appl. Pub. No. 2011/0007426).